In the past, as a method for producing a silica crucible for producing single crystal silicon for LSIs, the production methods described in Patent Literature 1 and Patent Literature 2 have been used. These methods are the methods by which, after quartz powder or synthetic cristobalite powder which was processed to be ultrapure is charged into a rotating mold and is molded, electrodes are pushed thereinto from above and voltage is applied to the electrodes to produce arc discharge, whereby the temperature of an atmosphere is raised to a melting temperature range (which is estimated to be about 1800 to 2100° C.) of the quartz powder to melt and sinter the quartz powder. However, since ultrapure quartz raw material powder is used in these production methods, these production methods are high in cost. Moreover, problems related to production cost and the quality of single crystal silicon has arisen, such as silicon monoxide (SiO) gas that is generated as a result of the reaction between molten silicon and a silica crucible when the produced silica crucible is used and is then taken into single crystal silicon as gaseous bubbles. Furthermore, there arises a problem of impurity contamination from the silica crucible, the impurity contamination which is the diffusion of impurity metal elements from a crucible wall when the single crystal silicon is pulled upwardly. In the following description, a silica crucible and a quartz crucible are synonymous with each other.
Moreover, in Patent Literature 3, a silica crucible having a three-layer structure formed of an outer layer made of natural quartz glass, an intermediate layer made of synthetic quartz glass containing a high concentration of aluminum, and an inner layer made of high-purity synthetic quartz glass based on an arc discharge melting method of silica powder raw materials (an atmosphere at the time of melting is estimated to be the air) is disclosed. In addition, the effect of preventing the movement of impurities (shielding effectiveness) by the intermediate layer is disclosed. However, in addition to the high cost of the three-layer structure, the problem of gaseous bubbles contained in the produced single crystal silicon is not solved.
Furthermore, in Patent Literature 4, a technique of reducing gaseous bubbles in a melted silica crucible wall by suction under a reduced pressure from the periphery of a molding die at the time of arc discharge melting of a silica powder raw material compact is disclosed. However, it is impossible to eliminate dissolved gas in the silica crucible wall completely only by sucking in the air present in a temporary compact of the silica powder under a reduced pressure. Moreover, there is a problem of SiO gas that is generated by the reaction between molten silicon and a silica crucible when the silica crucible is used and is taken into single crystal silicon as gaseous bubbles.
In addition, in Patent Literature 5, a quartz glass crucible that can prevent the generation of cavity defects called cavities (voids), non-through small-diameter holes (pinholes), and the like in a silicon wafer, the cavity defects caused as a result of SiO gas bubbles being taken into single crystal silicon, is disclosed. As a way of preventing it, providing projections and depressions formed as many scratches having a depth of 50 to 450 μm in at least part of the inner surface of a straight body portion and a curved portion of a crucible is disclosed. However, with such an irregular surface, degassing of the generated SiO gas to the outside of a silica container is inadequate, and, in particular, when a silicon single crystal has a large diameter of 12 inches (300 mm) or more, it is difficult to achieve a sufficient reduction of cavities (voids) and non-through small-diameter holes (pinholes) in a silicon wafer made by slicing and polishing such a silicon single crystal.
Moreover, also in Patent Literature 6, a quartz glass crucible that can prevent the generation of cavity defects caused as a result of SiO gas bubbles being taken into a silicon single crystal is disclosed. As a way, forming a region with high light transmittance in the bottom portion of a crucible is disclosed, whereby an increase in the temperature of the bottom portion is suppressed and it is possible to prevent the generation of SiO gas. However, inadequate suppression of the reaction between a quartz crucible and silicon melt is achieved by merely adjusting the light transmittance.
Furthermore, also in Patent Literature 7, similarly, an invention that can prevent the generation of cavity defects caused as a result of SiO gas bubbles being taken into a silicon single crystal is disclosed. As a way, setting a region with a high Al concentration in a bottom portion inner surface layer portion of a crucible is disclosed, whereby the viscosity of the bottom portion at a high temperature is increased and it is possible to prevent scratches and depressions reliably. However, since the Al concentration is in the high concentration range of 30 to 150 ppm, there arises a problem of an Al element taken into the produced single crystal silicon.